The present invention relates to a method of selectively forming an epitaxial film on a semiconductor substrate by using an insulating film as a mask and, more particularly, to a method of forming a selective epitaxial film which is improved not to form a facet on a selectively formed epitaxial film surface in contact with an insulating film.
Normally in selective epitaxial growth of silicon, an oxide film 42 is formed on the entire surface of a silicon substrate (to be referred to as a (100) silicon substrate hereinafter) 41 having a (100) plane as its surface, as shown in FIG. 1A.
Then, a rectangular opening portion 45 is formed in a desired portion of the oxide film 42 by etching. One side of the rectangular opening portion 45 is in the &lt;100&gt; direction.
A selective epitaxial film 43 is grown to fill the opening portion 45.
However, a (111) facet 44 having a (111) plane as its surface is undesirably formed on the surface of the selective epitaxial film 43 in contact with the oxide film 42, as shown in FIG. 1A.
Next, as shown in FIG. 1B, a polysilicon film 46 serving as, e.g., an electrode region is formed on the (100) silicon substrate 41 to cover both the oxide film 42 and the selective epitaxial film 43 having the (111) facet 44.
In this case, since the (111) facet 44 is formed, the (100) silicon substrate 41 and the polysilicon film 46 which are to be separated by the selective epitaxial film 43 undesirably contact each other and are rendered conductive, or the breakdown voltage therebetween undesirably decreases.
As one method to avoid this, Jpn. Pat. Appln. KOKAI Publication No. 6-260427 discloses the following method.
In this method, a (111) silicon substrate 51 is used, and a selective epitaxial film 53 is grown using an oxide film 52 as a mask, as shown in FIG. 2. According to this method, the surface energy of the (111) silicon substrate 51 having the (111) plane as a surface is low. For this reason, the selective epitaxial film 53 having a flat growth surface without any facet growth can be obtained as shown in FIG. 2.
In this method, however, the plane orientation of the silicon substrate 51 used for epitaxial growth is limited to the (111) plane. This method cannot be applied to the (100) plane used in normal semiconductor devices, and an application range becomes narrow.
As another method, Jpn. Pat. Appln. KOKAI Publication No. 5-182981 discloses the following method.
In this method, an oxide film 62 used as a mask for performing selective epitaxial growth on a (100) silicon substrate 61 is formed to have a special shape, i.e., a hang-over portion 64 on the interface side with a selective epitaxial growth film.
Thereafter, a selective epitaxial film 63 is epitaxially grown using disilane gas.
According to this method, the selective epitaxial film 63 having a flat surface can be obtained to fill a space defined by the side wall of the oxide film 62 and the lower surface of the hang-over portion 64 without any gap by the effect of disilane gas reflected by the lower surface of the hang-over portion 64, as shown in FIGS. 3B to 3D.
It is however very difficult to form the hang-over portion 64 on the oxide film 62.
As described above, it is difficult to obtain the selective epitaxial film 53 having a flat growth surface without any facet growth by using no mask of an oxide film in a special shape such as a hangover shape.